The present invention relates to a chain lock and more particularly to a chain lock assembly for securing a door in a partially open position.
A common chain lock assembly presently commercially available includes a length of chain having one end secured to a keeper bracket which can be attached to a door frame and the other end connected to a bolt for engagement with a slide bracket which can be attached to a door. The slide bracket usually includes an elongated slot for slidably receiving the bolt having an enlarged opening in one end to facilitate introduction of the bolt into the slot. A door equipped with a common chain lock assembly can usually be opened to a limited extent depending on the length of the chain when the bolt is in the end of the elongated slot remote from the enlarged opening.
The conventional chain lock assembly is designed to protect the occupants of a room, apartment, or home while the occupants are inside. The unfortunate experience of many has demonstrated that less than complete protection is provided, however, because a skilled intruder can sometimes slide the bolt along the elongated slot and through the enlarged opening by means of certain tools such as wires to gain access to the interior once the door has been opened the limited amount permitted by the chain. The chain can be shortened so that the door can be opened only slightly in an effort to avoid the problem of unauthorized entry. However, the occupants then find it difficult to open the door sufficiently to identify and speak with others on the outside. Accordingly, it has not been possible to enjoy maximum protection from the conventional chain lock assembly without unnecessarily limiting the otherwise significant utility of such devices.
The many advantages of the conventional chain lock assembly have lead to a search for ways to overcome the vexing problem of possible unauthorized entry by intruders. The result has been a number of structures such as those disclosed in U.S. Pat. Nos. 467,165; 1,492,030; and 3,155,410, but such structures have generally been complicated, unsuited for use with conventional chain lock assemblies, or simply inoperative. The present invention represents a distinct improvement in a simple, inexpensive bolt retention means which can quickly and easily be installed for use with any conventional chain lock assembly to effectively prevent unauthorized entry by intruders.